In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium to form characters and images. The ink-jet printing methods have been rapidly spread because of their various advantages such as easiness of full coloration, low costs, capability of using ordinary paper (plain paper, recycled paper) as the recording medium, non-contact with printed images and characters, etc.
Among such printing methods, in view of enhancing the weather resistance and water resistance of printed images and characters, an ink-jet printing method utilizing an ink containing a pigment as the colorant has now come to dominate (for example, refer to WO 00/39226, JP 8-157761A and JP 2003-183554A).
WO 00/39226 discloses a water-based ink containing a pigment-containing vinyl polymer.
JP 8-157761A discloses a water-based ink containing an oil film-forming component which is prepared by dissolving a water-insoluble resin therein in order to suppress color bleeding. However, since the water-insoluble resin must be dissolved in the ink, a content of the water-insoluble resin in the ink is small, so that the resultant ink fails to exhibit a sufficient function.
JP 2003-183554A discloses an ink containing 10 to 1000 ppm of a phthalic diester and a latex in order to form images having a good gloss. However, since a content of the phthalic diester in the ink is small, the resultant ink fails to exhibit a sufficient function.
JP 2004-75759A discloses a dispersion of colored fine particles containing a microcapsule formed by incorporating a hydrophobic pigment, a hydrophobic polymer and a high-boiling organic solvent in urethane particles.
JP 2003-147236A discloses a pigment-containing ink for ink-jet printing in which a total content of aliphatic acid derivatives in the ink is 1.0% by mass or lower, and the pigment particles are respectively coated with a water-insoluble polymer.
However, the pigment-containing ink is unsatisfactory in gloss, image clarity, etc.